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H. S. Kim H. R. Harrison P. G. Winchell 《Metallurgical and Materials Transactions A》1981,12(8):1461-1465
Experimental measurements of hardness, optical microstructure, and austenite lattice parameter were carried out on samples
cooled to — 196 °C to form martensite and reheated for 1 h at 100 to 1200 °C. Reheating first results in depletion of carbon
from the martensitic matrix and in formation of a small amount of austenite and for temperatures above 400 °C it results in
secondary hardening presumably due to the formation of low-nickel cementite. Above 600 °C the low-carbon matrix reverses to
austenite whose carbon content is determined by the metastable carbon and nickel equilibration of austenite and cementite.
Between 700 °C and 800 °C graphite forms and cementite disappears; concurrently the austenite recrystallizes. Above 900 °C
the austenite carbon level follows the stable austenite graphite equilibrium.
formerly Visiting Professor at Purdue University, is currently Professor of Materials Engineering, Jeonbug National University,
Seoul, Korea. 相似文献
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Alloying element partition and growth kinetics of proeutectoid ferrite in deformed austenite were studied in an Fe-0.1C-3Mn-1.5Si
alloy. Very small ferrite particles, less than several microns in size, were formed within the austenite matrix, presumably
at twin boundaries as well as at austenite grain boundaries. Scanning transmission electron microscopy–energy-dispersive X-ray
(STEM-EDX) analysis revealed that Mn was depleted and Si was enriched in the particles formed at temperatures higher than
943 K (670 °C). These were compared with the calculation of local equilibrium in quaternary alloys, in which the difference
in diffusivity between two substitutional alloying elements was assumed to be small compared to the difference from the carbon
diffusivity in austenite. Although the growth kinetics were considerably faster than calculated under volume diffusion control,
a fine dispersion of ferrite particles was readily obtained in the partition regime due to sluggish growth engendered by diffusion
of Mn and Si. 相似文献
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《Acta Metallurgica》1987,35(5):1007-1017
The interphase boundary structure and interface processes at the pearlite-retained austenite growth interface in Fe-0.8 wt% C-12 wt% Mn alloy have been investigated by transmission electron microscopy. Facetting, misfit correcting dislocations, and ledge defects are all observed at the previously assumed disordered boundary. Hot stage electron microscopy revealed that the ledge defects are mobile, indicating the migration of the growth interface occurs by the lateral movement of steps. It is found that the growth ledges are continuous across the growth interfaces of the pearlitic ferrite and cementite. This provides a mechanism by which the interface processes of the two pearlite phases may be coupled. 相似文献
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R. E. Hackenberg D. G. Granada G. J. Shiflet 《Metallurgical and Materials Transactions A》2002,33(12):3619-3633
The kinetics, morphology, and elemental distributions associated with the decomposition of austenite in Fe-0.30C-6.3W were
surveyed, especially in the bay region of the time-temperature-transformation (TTT) diagram. Carbide precipitation characteristics
were of particular interest. Similar to Fe-C-Mo and Fe-C-Cr alloys, grain- and twin-boundary bainite containing sheets of
alloy carbides dominated the microstructure at and above the bay, while popcorn-like bainite was observed immediately below
the bay. Nonequilibrium carbide-phase combinations were obtained both above and below the bay, although W partitioning to
the alloy carbides was always observed. The carbon level in the remaining austenite increased with reaction time at a given
temperature, which, at the later stages of reaction, helped trigger the growth of a constituent containing a high density
of nonlamellar carbides. These nonequilibrium reaction-path characteristics are considered to originate from crystallographic
and interfacial structure constraints affecting the nucleation of carbides at ferrite-austenite interfaces. 相似文献
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The effect of thermomechanical control processing(TMCP)on microstructure and mechanical properties of Fe-0.2C-1.44Si-1.32Mn hot rolled TRIP steel was investigated through experiments.Strain-induced transformation and transformation-induced plasticity behavior of retained austenite were analyzed.The results show that with multipass deformation,reduction per pass of more than critical deformation in austenite recrystallization region and total reduction of more than 58% in non-recrystallization region and high temperature section of two-phase region,austenite can be refined before γ→α transformation.It is beneficial to obtain refined ferrite grain in final microstructure.To obtain fine and uniform microstructure and excellent strength-ductility balance,a three-stage cooling process(laminar cooling-air cooling-ultra-fast cooling)after hot rolling was conducted.The ultimate tensile strength and elongation of the investigated steel can reach 663 MPa and 41%,respectively. 相似文献
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G. H. Zhang R. Wei M. Enomoto D. W. Suh 《Metallurgical and Materials Transactions A》2012,43(3):833-842
The growth kinetics of proeutectoid ferrite in the early stages of transformation were studied in Fe-0.1C-1.5Mn-1Si (mass
pct) quaternary and Fe-0.1C-1.5Mn-1Si-0.2Al quinary alloys. The observed kinetic transition temperatures from partitioned
slow growth to unpartitioned fast growth of ferrite in both alloys are in good agreement with predictions using a local equilibrium
model for multicomponent systems. The measured parabolic growth rate constants were smaller than those calculated assuming
paraequilibrium in the unpartitioned growth region, but the difference between the measured and the calculated growth rate
constants gradually diminished with a decreasing reaction temperature. The dissipation of driving force, derived from the
diffusion of the substitutional solute within the transformation interface, possibly constitutes a major part of the discrepancy
between the measured and the calculated growth kinetics. 相似文献
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Rangasayee Kannan Yiyu Wang Leijun Li 《Metallurgical and Materials Transactions A》2017,48(3):948-952
A unique dilatation trend is observed for isothermal bainite transformation in Fe-0.84 pct C-1 pct Cr-1 pct Mn steel. The dilatation is found to occur in two stages with volumetric contraction dominating the first stage, followed by volumetric expansion dominating the second stage. Through electron microscopic characterization, bainitic microstructure is identified as inverse bainite with cementite (Fe3C) nucleating first from supersaturated austenite followed by the transformation of ferrite and secondary carbides (Fe3C, Fe2C, and Fe5C2) from carbon-depleted austenite. 相似文献
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Cen Qiongying Wang Weijun Zhang Bendao Yan Zijie Wang Yang Zhang Mei 《Metallurgical and Materials Transactions A》2022,53(11):4034-4046
Metallurgical and Materials Transactions A - The influence of Ni addition on the microstructure evolution and mechanical properties of Fe–0.2C–3.5Mn medium Mn steel after intercritical... 相似文献
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The behavior of inclusions in the process of B-phase growth during the solidification of Fe-0.15C-0.8Mn steel was in-situ observed using a high-temperature confocal scanning laser microscope (HTCSLM). ... 相似文献
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Growth kinetics of proeutectoid ferrite, including grain boundary face nucleated ferrite, grain boundary edge nucleated ferrite allotriomorph and intragranular ferrite idiomorph, were experimentally measured in an Fe- 0.09C-1.5Mn-0.2Si steel and compared with theoretical calculation in local equilibrium and paraequilibrium modes. Grain boundary edge nucleated ferrite exhibited larger growth rate than grain boundary face nucleated ferrite and in- tragranular ferrite idiomorph. Experimental kinetics of proeutectoid ferrite was within the window defined by the lo- cal equilibrium and paraequilibrium limits. A transition of growth kinetics from paraequilibrium to local equilibrium was observed in the temperature range of 650--750 ℃, which can be explained in terms of solute drag. 相似文献
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The effects of initial microstructure and thermal cycle on recrystallization, austenite formation, and their interaction were studied for intercritical annealing of a low-carbon steel that is suitable for industrial production of DP600 grade. The initial microstructures included 50 pct cold-rolled ferrite–pearlite, ferrite–bainite–pearlite and martensite. The latter two materials recrystallized at similar rates, while slower recrystallization was observed for ferrite–pearlite. If heating to an intercritical temperature was sufficiently slow, then recrystallization was completed before austenite formation, otherwise austenite formed in a partially recrystallized microstructure. The same trends as for recrystallization were found for the effect of initial microstructure on kinetics of austenite formation. The recrystallization–austenite formation interaction accelerated austenization in all the three starting microstructures by providing additional nucleation sites and enhancing growth rates, and drastically altered morphology and distribution of austenite. In particular, for ferrite–bainite–pearlite and martensite, the recrystallization–austenite formation interaction resulted in substantial microstructural refinement. Recrystallization and austenite formation from a fully recrystallized state were successfully modeled using the Johnson–Mehl–Avrami–Kolmogorov approach. 相似文献
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The progress of the martensite (α′) to austenite (γ) phase transformation has been thoroughly investigated at different temperatures during the continuous heating of a cold-rolled precipitation hardening metastable stainless steel at a heating rate of 0.1 K/s. Heat-treated samples have been characterized using different experimental complementary techniques: high-resolution dilatometry, magnetization, and thermoelectric power (TEP) measurements, micro-hardness-Vickers testing, optical/scanning electron microscopy, and tensile testing. The two-step transformation behavior observed is thought to be related to the presence of a pronounced chemical banding in the initial microstructure. This banding has been characterized using electron probe microanalysis. Unexpectedly, dilatometry measurements seem unable to locate the end of the transformation accurately, as this technique does not detect the second step of this transformation (last 20 pct of it). It is shown that once the starting (A S) and finishing (A F) transformation temperatures have been estimated by magnetization measurements, the evolution of the volume fractions of austenite and martensite can be evaluated by TEP or micro-hardness measurement quite reliably as compared to magnetization measurements. The mechanical response of the material after being heated to temperatures close to A S, A F, and (A F ? A S)/2 is also discussed. 相似文献
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E. S. Humphreys H. A. Fletcher J. D. Hutchins A. J. Garratt-Reed W. T. ReynoldsJr. H. I. Aaronson G. R. Purdy G. D. W. Smith 《Metallurgical and Materials Transactions A》2004,35(4):1223-1235
A scanning transmission electron microscope (STEM) technique was used to measure Mo concentrations at ferrite:austenite (α:γ) interfaces in an Fe-0.24 pct C-0.93 pct Mo alloy partially transformed at 650°C, 630°C, and 610°C. These concentrations
were quite small at 650°C, which is just below the bay temperature of the time-temperature-transformation (TTT) curve for
the initiation of ferrite formation. There were larger concentrations at 630°C, a temperature at which transformation stasis
(incomplete transformation) occurred. Concentrations at 610°C were intermediate between the values observed at 650°C and 630°C.
The average accumulation at the latter temperatures increased appreciably as a function of transformation time. After each
heat treatment, there was considerable variation in Mo accumulation from one α:γ interface to another and, to a lesser extent, from one region to another along the same interface. These higher Mo concentrations
were deduced to have developed largely through volume diffusion of Mo, mainly through ferrite, to interfaces whose ledgewise
growth had been interrupted by growth stasis. (Mo2C precipitation at α:γ boundaries occurred only at the end of growth stasis.) It appears that only a very small amount of Mo segregation is needed,
probably at specific interfacial sites, in order to produce growth cessation. Growth kinetics anomalies of this kind continue
to provide the best evidence available for the operation of a coupled-solute drag effect.
This article is based on a presentation given in the symposium “The Effect of Alloying Elements on the Gamma to Alpha Transformation
in Steels,” October 6, 2002, at the TMS Fall Meeting in Columbus, Ohio, under the auspices of the McMaster Centre for Steel
Research and the ASM-TMS Phase Transformations Committee. 相似文献
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The behavior of inclusions in the process of δ-phase growth during the solidification of Fe-015C-08Mn steel was in-situ observed using a high-temperature confocal scanning laser microscope (HTCSLM). The results show that inclusions arrive the S/L (solid/liquid) interface by way of direct impact or gradual drift, when the cell spacing is approximately equal to 177 μm during the growth of cellular δ-phase. The inclusions easily stay at the positions of trailing vortex formed by the circumferential motion of molten steel around δ-phase. Some inclusions reaching the S/L interface are captured by the solid-phase. Some of them move along the normal direction of the S/L interface because of pushing of solid-phase, and the others get away from the S/L interface after being pushed for a distance. The faster the growth rates of the solid-phase are, the easier the inclusions are captured by the S/L interface. The slower the growth rates of the solid-phase are, the easier the inclusions move with the S/L interface. 相似文献